A major unsolved problem in biology is what causes senescence. We plan to investigate the control of senescence using the observation that males and females, in both C. elegans and D. melanogaster, show differential longevity, with the homogametic sex living longer. This phenomenon will be exploited in two ways: 1) by generating gynandromorphs, determining which tissue are XX and which are XO, and then correlating these tissues with the life-span of the individual, 2) by using genes which cause sex transformation to change the sexual phenotype of the individual and then determining the longevity of these transformed individuals. We hope to answer two basic questions: 1) Is this differential sexual longevity controlled by the genotype or the phenotype? 2) Which tissue(s) are most responsible for differential sexual longevity?